Cross-talk attenuating supply air and exhaust air device in ventilation installations

ABSTRACT

A device for supplying or exhausting air in the rooms of a multiple-room building having a central system with ducts common to several rooms. The device is a chamber which has a convergent tubular inlet frustum for delivering a stream into the chamber, and an outlet opening for delivering the air from the chamber. A silencer passageway is between the smaller open end of the tubular frustum and the outlet opening for attenuating crosstalk. The passageway is preferably surrounded by sound-absorbing material such as mineral wool.

United States Patent 1 1 La' irkfeldt et al.

11] 3,759,157 1Sept. 118, 1973 CROSS-TALK ATTENUATING SUPPLY AIR AND EXHAUST AIR DEVICE IN VENTILATION INSTALLATIONS [75] Inventors: Iirger La'irkieldt, Bamap; Stellan Akesson; Ingmar Josefsson, both of Jonkoping, all of Sweden [73] Assignee: Alrtiebolaget Svenska Flaktfabriken, Necka, Sweden [22] Filed: Dec. 1, 1971 [21] Appl. No.: 203,533

[30] Foreign Application Priority Data Dec. 17,1970 Sweden ..17175/7o 52 US. Cl. 98/37, 98/40 N, 181/47 R 511' Int. Cl F24f 7/00 58 Field of Search 181/47 R, 47 A, 48, J 181/70; 98/40 N, 40 D, 40 DS, 37

[5 6] References Cited UNITED STATES PATENTS 1,754,411 4/1930 Balduf 98/DIG. 7

2,725,948 12/1955 Keene 181/47 R 2,855,068 10/1958 Chapel 181/47 R 1,811,762 6/1931 Schnell 181/47 2,229,119 l/194l Nichols et a1. 1. 181/47 R FOREIGN PATENTS OR APPLICATIONS 1,102,371 3/1961 Germany 98/49 Primary Examinerwilliam E. Wayner Assistant Examiner-William E. Tapolcai, Jr. Attorney-Howson & Howson 57 ABSTRACT A device for supplying or exhausting air in the rooms of a multiple-room building having a central system with ducts common to several rooms; The device is a chamber which has a convergent tubular inlet frustum for delivering a stream into the chamber, and an outlet opening for delivering the air from the chamber. A silencer passageway is between the smaller open end of the tubular frustum and the outlet opening for attenuating cross-talk. The passageway is preferably surrounded by sound-absorbing material such as mineral wool.

10 Claims, 5 Drawing Figures PATENTEQSEPIBW 5.759.151 SHEET 1 [IF 2 PATENTED SEP] 8 I975 SHEET 2 [IF 2 Fig .3a

T CROSS-TALK ATTENUATING SUPPLY AIR AND EXHAUST AIR DEVICE IN VENTILATION INSTALLATIONS This invention relates to a cross-talk attenuatingsupply air and exhaust air device for use in ventilation installations, particularly high-pressure installations for comfort ventilation with distribution air and return air passageways common to the different rooms connected to a ventilation unit.

In a modern type of comfort ventilation installations, the air. to the different rooms connected to the ventilation unit is distributed via main passageways common to the rooms, thereafter through branch passageways from said main passageways and, finally, via supply air devices into the rooms in question. The stale air, in an analogous manner, is removed through exhaust air devices and passageways connected to each room and further through common exhaust air passageways to the fan unit where the air is subjected to further treatment and cleaning and possibly re-circulated.

For making the air flow to or from a room independent of the air flow to or from other rooms connected to the same main passageway, the components of the installation are dimensioned according to the so-called control ventilation principle disclosed in the Swedish patent No. 170,566, in such a manner, that the major air resistance is generated in the supply air and exhaust air devices, and the main and branch passageways offer only insignificant resistance to the air flow.

The supply air and exhaust air devices, thus, in addition to the primary requirement of small dimensions, also must meet the requirement of being. designed such as to offer a given resistance to a given air flow passing therethrough. The simplest way of satisfying both requirements is by making a hole in a plane wall, but it has the disadvantage that the air stream passing through the hole produces highly disturbing blowing noises. This solution, therefore, is not attractive to the constructor. When, however, the hole is provided with a supply passageway having across-section continuously decreasing in the direction of the air flow, the blowing noise is reduced and, by a suitable choice of the degree of taper of the passageway, the noise can be lowered to an acceptable level. The supply air and exhaust air device hereby comprises a hollow truncated cone or pyramid with its base (the large end) facing the air flow. The resistance to the air flow is determined substantially entirely by the size of the opening in the top (the small end) of the hollow frustum. For passing a desired air flow through the supply air device, an overpressure in the common distribution passageway is required which is higher than that in ventilation installations comprising individual distribution passageways. Therefore, the type here referred to is defined as a high-pressure installation.

These high-pressure installations, however, show a phenomenon, which usually cannot be tolerated, viz. cross-talk of spoken words and other sound between the different rooms, caused by the common passageways constituting acoustic connection links between the rooms.

Cross-talk, which is most apparent when the air flow in system is interrupted, can be counteracted by a sound attenuating filter in the passageways which does not appreciably obstruct the air flow, but very well obstructs or attenuates the sound waves therein. The

sound filters, in order not to increase the air resistance of the common passageways, are connected to the supply air and exhaust air devices. Thereby the filters are subject to the same requirements as said devices, viz. to have small dimensions.

A usual sound filter is the so-called chamber silencer which, as indicated by its name, comprises a closed chamber with inlet and outlet openings. Sound waves entering through either of these openings are after repeated reflections against the chamber walls attenuated and only a residual part of them continue out through the other opening. This residual part decreases with increasing cross-sectional area and length of the chamber for any given inlet and outlet openings. The primary requirement of small dimensions, however, soon produces an upper limit to the size of the chamber.

For constructional reasons, preferably a simple geometric form is to be chosen for the chamber and its connected passageways, for example the form of a cylinder or a parallele-piped. However, the air flowing through such a silencer chamber produces an unacceptable blowing sound.

The present invention satisfies the aforesaid requirements of the supply air and exhaust air devices and of the sound filter, viz:

small dimensions necessary resistance to the air flow absence of blowing noise, and

necessary attenuation of cross-talk- The device according to the invention is a combination in one unit of a supply air and exhaust air device and a sound filter, which unit is characterized in that it comprises a closed chamber, into which projects an inlet pipe in the form of a truncated cone or pyramid having its base (large end) in one end wall of the chamber. The other chamber end wall has a hole of at least such a size as to prevent the air jet delivered from the mouth (small end) of the inlet pipe as a stream separate from the surrounding air from interfering with the hole edges and thereby from producing a disturbing blowing noise.

It was found that the inlet projecting into the chamber changes the noise-reflection paths in the chamber such, that the attenuation is improved substantially over the attenuation effected in the conventional chamber silencer with plane end walls.

The attenuation can be improved still more according to a suitable embodiment, by filling that space in the chamber through which the air stream does not flow with a sound-absorbing material, for example min eral wool.

The assemblage of the supply air or the exhaust air device with the sound filter as oneunit renders possible a saving of space compared with a separate mounting of said components, but it also provides the entirely novel and surprising technical effect, that the assemblage has proved to increase the attenuation by the sound filter and thereby renders possible a reduction of the unit dimensions.

The invention is described in greater detail in the following, with reference to the accompanying drawings, in which FIG. 1 shows a basic sketch of a device equipped as a supply air device,

FIG. 2 shows a basic sketch of the device of FIG. I equipped as an exhaust air device, and

FIGS. 3a, b, and c show a face view and two sections on lines AA and BB respectively of an adjustable exhaust air device.

H08. 1 and 2 show the idea of the invention in a basic layout. A closed chamber 1 has an inlet pipe 2 designed as a truncated cone or a truncated pyramid, the base and top of which may be of square or rectangular shape. The outlet opening 3 is aligned with the axis of the inlet frustum, and is of such a width that the air stream indicated by dashed lines 8 does not interfere with the edges of the opening. In FIGJ a duct 4 for the supply air is connected to the chamber by a flange 4a and in FIG. 2 a duct 5 for the exhaust air is connected to the chamber by a flange 5a.'A sound-absorbing material 6 for example mineral wool is provided in the chamber 1 away from the stream of air shown at 8. The mounting wall surface is indicated by 7.

FIG. 3 shows by way of an example an application of the invention to an exhaust air device with adjustable measurements and illustrating the optimum angular relationships. FIG. 3a shows a view of the device seen from the ventilated room. The chamber 11 is here of square section. The inlet pipe 12 has the shape of a truncated pyramid with rectangular base and top. One of the sides, 13a, is here laterally so displaceable, by means of a handle 13b that the air resistance of the pipe can be adjusted. The inclinations of the sides of the inlet pyramid indicated by the angular values 40 and 65 have proved to produce a minimum of noise, by measurement.

We claim:

1. A cross-talk attenuating supply air and exhaust air device in ventilation installations comprising a box for connection to a distribution duct of the installation having opposite end walls spaced apart to provide a closed chamber, said end walls having aligned openings therein, an inlet pipe in the form of an open-ended tapered element with the large end fitted into the inlet opening in one end wall of the chamber and with the small end projecting into the chamber toward the outlet opening in the other end wall, said pipe being shorter than said chamber whereby its small end terminates in spaced relation to said outlet opening in the other chamber end wall, said opening consisting of a hole larger than said small end and being positioned so that the air jet delivered from the small end of the inlet pipe as a stream separate from the surrounding air passes through said hole and is prevented from interfering with the hole edges and thereby from producing disturbing blowing noise.

2. A cross-talk attenuating supply air and exhaust air device according to Claim 1 characterized by a soundabsorbing material in the interior of said chamber surrounding the large end of the inlet pipe and spaced from the terminus of said pipe and spaced from the hole edges and contoured to avoid interfering with the air jet stream delivered from said inlet pipe.

3. A device according to claim 2 wherein said material is mineral wool.

4. A device according to claim 1 including means to connect the chamber to a high-pressure system for comfort ventilation comprising distribution and return air ducts common to different rooms and connected to a central unit.

5. A device according to claim 4 wherein said device is a supply device and said connecting means connects the large end of said inlet pipe to the distribution air duct.

6. A device according to claim 4 wherein said device is an exhaust device and said connecting means connects the outlet opening of said chamber to the return air duct.

7. A device according to claim 1 wherein said inlet pipe is in the form of an open-ended rectangular pyramid having convergent side walls of a greater length than the width of the convergent end walls.

8. A device according to claim 7 wherein one of said side walls is laterally displaceable to afford adjustment of the air resistance of the inlet pipe.

9. A device according to claim 7 wherein said side walls converge with an included angle which is substantially less than the included angle of the converging end walls.

10. A device according to claim 9, wherein the included angle of the side walls is approximately 40 and the included angle of the end walls is approximately 65. 

1. A cross-talk attenuating supply air and exhaust air device in ventilation installations comprising a box for connection to a distribution duct of the installation having opposite end walls spaced apart to provide a closed chamber, said end walls having aligned openings therein, an inlet pipe in the form of an openended tapered element with the large end fitted into the inlet opening in one end wall of the chamber and with the small end projecting into the chamber toward the outlet opening in the other end wall, said pipe being shorter than said chamber whereby its small end terminates in spaced relation to said outlet opening in the other chamber end wall, said opening consisting of a hole larger than said small end and being positioned so that the air jet delivered from the small end of the inlet pipe as a stream separate from the surrounding air passes through said hole and is prevented from interfering with the hole edges and thereby from producing disturbing blowing noise.
 2. A cross-talk attenuating supply air and exhaust air device according to Claim 1 characterized by a sound-absorbing material in the interior of said chamber surrounding the large end of the inlet pipe and spaced from the terminus of said pipe and spaced from the hole edges and contoured to avoid interfering with the air jet stream delivered from said inlet pipe.
 3. A device according to claim 2 wherein said material is mineral wool.
 4. A device according to claim 1 including means to connect the chamber to a high-pressure system for comfort ventilation comprising distribution and return air ducts common to different rooms and connected to a central unit.
 5. A device according to claim 4 wherein said device is a supply device and said connecting means connects the large end of said inlet pipe to the distribution air duct.
 6. A device according to claim 4 wherein said device is an exhaust device and said connecting means connects the outlet opening of said chamber to the return air duct.
 7. A device according to claim 1 wherein said inlet pipe is in the form of an open-ended rectangular pyramid having convergent side walls of a greater length than the width of the convergent end walls.
 8. A device according to claim 7 wherein one of said side walls is laterally displaceable to afford adjustment of the air resistance of the inlet pipe.
 9. A device according to claim 7 wherein said side walls converge with an included angle which is substantially less than the included angle of the converging end walls.
 10. A device according to claim 9, wherein the Included angle of the side walls is approximately 40* and the included angle of the end walls is approximately 65* . 